The present invention relates to a frictionless hydraulic damper.
By way of background, frictionless hydraulic dampers are desired for certain applications to attenuate forces between relatively movable objects where the internal frictional resistance of the dampers is objectionable. By way of specific example, in nuclear plants small pipes are suspended by hangers in the nature of dampers which are subjected to forces within the 200 to 3,000 pound range. In the past it has been highly impractical to use hydraulic dampers for this application for two reasons. Firstly, radiation affected the plastic or rubber seals and thus permitted them to leak. Secondly, seals create friction, and where small pipes were suspended by dampers which were subjected to forces between 200 and 500 pounds, the seal friction was a substantial portion of the applied forces and thus did not allow the small pipe to move in an unrestrained manner while being supported. Therefore, in the past hydraulic dampers were not used for the foregoing applications, and instead highly complex mechanical snubbers were used. These required high maintenance and many times were unreliable because of their complexity.
In order to overcome the foregoing deficiencies, the devices of U.S. Pat. No. 4,638,895, dated Jan. 27, 1987 and of copending U.S. patent application Ser. No. 6,365 filed Jan. 23, 1987 were devised. There prior devices utilized piston rod seals in the nature of labyrinth seals or bushings in both end walls of a cylinder and a bellows member connected between each of the end walls and the portions of the piston rods outside each of the end walls to contain leakage of hydraulic fluid past the seals or bushings. In addition, the piston rod included ductwork for conducting the hydraulic fluid between the two bellows members at opposite ends of the cylinder. The location of the bellows members caused the prior dampers to be relatively long, which limited their use to spaces which could accept them. Furthermore, the fluid circuit through the piston rod constituted additional structure, and further the additional volume of the bellows required additional hydraulic fluid.